Tubular rudder



Aug. 20, 1957 R. w. ERLBACHER 2,303,211

TUBULAR RUDDER Filed Feb. 21. 1955 2 mails-sheet 1 2 0, 1957 R, wERLBACHER 2,803,211.

TUBULAR RUDDER 'Filed Feb. 21, 1955 2`Sheets8heet 2 /A/l/E /7'OR: ROBERTW. ERL @nef/5e) .5y ,wir

nited States Patent Office TUBULR RUBBER Robert W. Erlbacher, CapeGirardeau, Mo. Applieaann February 21, 195s, serial. No... 489,586.

4 Claims. (Cl. 114-166).

This invention relates. to a tubular rudder'for marine use... and-'inparticular is concerned with, a. tubular rudder which is pivotedf aft ofthe propeller.

In` the past, blade rudders have been conventionally used behind apropeller on marine vessels for steering. These rudders have beenobjected to inA varying degree because of vibration, excessive powerrequiredin, steer. ing, poor etliciency in ysteering which is reflectedlinpoor maneuverability andA extremely turbulent wash. The rst three ofthese features are reliected in disadvantages in ship operation whichnecessitates rugged construction. and control devices. The last feature,the turbulent wash, is.. dangerous to surrounding small craft which areoften capsized when. a vesesl. of substantialy proportions is in theneighborhood.

Attempts have been made in the past to obviate the diilicultiesfound. inthe blade rudder, and one such attempt to this problem resulted intheKort rudder. The Kort rudder consisted of a tubular shell positionedaround a propeller wheel with a very small clearance for the wheel; justsuicient for the wheel to fit within the rudder. Although the turbulentwash was reduced by theKort rudder, it has still left certaindesirable-.features to/be obtained relative to vibration, easiersteering, which is reected in less torque onI the rudder stem, andgreater maneuverability.

By means. ofthis. invention there has been provided a tubular rudderwhich is pivoted aft and spaced from the propeller-wheel. Thisrudderreceives the fullforce and extent. of the water propelled through thepropeller Wheel inside the. shell of the rudder and passesit. outwardlythrough a rear opening in such a manner as. to fully enclose andcontrolthe propelled race. The rudder is of slightly smaller internal diameterthan the propeller. wheel to accommodate the reduced diameter of thejetl stream of water propelled from the propeller which, un. dergoes aslight contraction after leaving the propeller.

Thus, afull control and enclosure of this propelled water is obtained.

Preferably, the. rudder is also of an airfoily designin. its wallsectionwith the internal diameter ilaring some.. what at the frontbehind the propeller wheel. Also, the leadingfront edges of theA rudder`are` recessed at. the sides between the top and bottom to provide for.greater cross section of entry when the rudder is pivoted away froml thestraight` position either to port or starboard whereby greatersteeringcontrol is obtainable.

- It has been foundrthatby the use of this invention the vibration. and.steering. power requirements have been. decreased, and maneuverabilityorl response to rudder; position has been improved. The actual thrustfrom the propeller obtainedA by the usek of the tubular rudder; of; thisinvention, also has been increased-over thel pre. viously knownbladerudders, and the Kort rudder. Further-maintenance of the propellershaft is facilitated by. use of the .tubular rudder since the rudderneedV not bedisnrantled for, removalofthe shaft. Likewise, the wake`or.,VV wash behind the tubular. rudderr of this invention has PatentedAug. 20, 1957 been reducedA to.` a smooth, even roll so as to facilitatemarine tracin; the neighborhood. of the shipV equipped with thisinvention` whereby marine hazards have been greatly minimized.

Accordingly, it is a principal object of thisA invention to provide atubular rudder situated. aft of the vessels propeller wheel to obtainincreasedV operating benefits.

Another object of this invention is to provide a tubular rudder aft of apropeller wheel: in which therudderhas an airfoil wall design.

A further object of thisinvention istofprovidea tubular rudder which hasrecessed side portions. on its front end so that it can be pivoted.behind a propeller'and receive a maximum ow of race therefromy forincreased maneuverability. and steeringY efficiency;

Still another object' of this invention is: to provide ak tubularrudder` aft of la propeller wheel which is ofi a reduced size withrespect to said Wheel for a full con trol of the wheel race for the,Apresentation of a restricted opening to. accommodate the propeller race.

Still; a further. object of this invention is to provide a reduced.draft tubulary rudder spaced' aftv ofv a propeller which reducesvibration.

Still anothen object of this. invention is toprovide al tubular ruddenspaced. aft of the propellerwhich-increases forward. thrust.y of thevessel andV reduces engineload Still another object of this invention isto provide a: tubular rudder. spaced: aft offa propeller which increasesmaneuverability of the vessel; and reduces power required formaintaining.v theV rudder in a desired position.

Still another object of' this. invention is to. provide ay tubularrudder spacedfaft'of. a. propeller whichvvdoes notf increase the draftofthe vessel. andv c an-l be used withi standard steering. and propellerrigs.y

Still azfurtherA object of` this invention is to provide aA tubularVrudder whichy provides a: minimum of flow re-r striction of Waterpresented to the propeller whenthe.

engines are reversed so that high efficiency can be obtainedfin backing.

It is still a further object off this invention. toprovide a tubularrudder spaced aft of a propeller to produce` asmooth wash, andltherebylessen thehazardl presented to small-boats in the neighborhood. v

vIt is stilly another object of this` invention to providea tubularrudder which is adapted for use with=conve1r tional vessels and canbeeasily installedand maintained,v

be had to the accompanying drawings'showing, preferred embodiments of,this invention. It isto be understood,

however, thatthesedrawings are for the purpose ofillus tration only,andthat. the invention is not limited thereto..

In lthe drawings:A

Figure 1 is aviewinside elevation` of a propellerl equippedvesselprovidedwtihkthe.tubular rudder. of this invention which ispartiallybrokenaway toshow theside.

wall construction;`

FigureZis .a somewhat enlargedviewshowing the pro-v peller and ruddercombinationwith. thefl'ow streamsof the propellerV raceindicated indotted` lines;`

Figure isa View similar,- to FigureZ, but showing the l rudder in thehard port position with the changed flow lines of the race;

Figure 4 is a view in front elevation of the propeller looking backthrough the rudder of Figure 2;

Figure 5 is a force diagram showing the eifect of depth below the watersurface on the propeller race;

Figure 6 is a view similar to Figure 4 showing a modied form of rudder;

Figure 7 is a view partially broken away in side elevation of themodified rudder of Figure 6; and

Figure 8 is a view similar to Figure l showing the employment of abacking rudder positioned forwardly of the propeller.

In Figure l, a vessel 10 is shown equipped with a conventionalmultibladed propeller 11 affixed to a propeller shaft 12 which isjournaled within a bearing support 13. The tubular rudder is generallyindicated at 14 and is spaced aft of the propeller. A rudder post orstem 15 is fixed to the rudder and extends vertically within the vesselwhere its pivotal operation is controlled in a known manner.

The propeller 11 is preferably equipped with a fairwater 18 which tendsto equalize out the flow lines in the race of wash aft of the propellerin order to reduce turbulence. The force lines of the race are shown at16 in Figure 2 where it can be seen that the fluid flowing through thepropeller wheel and which is Worked upon by the blades of the wheel ispropelled aft of the wheel in the form of a generally cylindrical jet ofextremely high velocity. Actually the cross-sectional shape is notexactly cylindrical as will be made more apparent hereinbelow. Thisgenerally cylindrical wheel race undergoes a partial contraction aft ofthe wheel or a necking-down to a point just behind fairwater where itevens out to a subsequently constant cross section until quite somedistance behind the propeller (not shown) the force is dissipated. Thediagrammatic showing of the force lines in the propeller race of Figure2 represents the standard condition of a heavily loaded propeller wheelrace independent of the use of any rudder at all.

. This substantially cylindrical wheel race is enclosed by the tubularrudder 14 to attain full effects in thrust, maneuverability, andsteering power requirements, while at the same time vibration isminimized through the rudder post 15 to the vessel. To effectuate theenclosing of the race, the rudder is made of the approximate internaldiameter of the neck-down race after the race is contracted at point 17.

To determine this diameter the following procedure is followed. Thecross-sectional area of each blade is obtained at its thickest part.This area is multiplied by the number of the blades and then added tothe cross-sectional area of the propeller hub at the thickest part ofthe blades. This sum is then subtracted from the total propeller area.Lastly, for heavily loaded screws an additional 15% is subtracted as theslippage is fairly high while with more lightly loaded screws thispercentage can be decreased. This diameter is generally about 80 to 90%of the diameter of the propeller wheel and varies somewhat dependingupon the propeller design and the load placed upon it, as is understoodin the art.

As is apparent from Figures 2 and 4, the tubular rudder 14 has an openfront end 20 and rear end 21. The rudder is supported behind thepropeller by the rudder stem 15 which is xed to the rudder 14. The pivotpoint is spaced behind the propeller a distance approximately equal tothe diameter of the propeller at a point approximately where thenecking-down of the propeller race is completed. It will be noted thatthe top portion 23 and bottom portion 24 of the front end 20 extendforwardly of the pivot or rudder post 15, while the port side portion 25and starboard portion 26 are both recessed with respect to the top andbottom portions. Thus, both side portions 2S and 26, as shown in Figure2, are cnt back about to the rudder stem. This provides for greateraccess of entrance when the rudder it turned to the hard port position,as shown in Figure 3 where the force lines of the propeller race aregiven greater access of entry due to the recessed portion 25. Obviouslythis also applies to the starboard positioning of the rudder throughrecessed portion 26.

A modification of this design is shown for the rudder 14 in Figure 8where the front bottom wall is cut back in relation to the top toprovide a lower front end portion 29, which is more or lessstraight-edged about the lower half of the rudder. This design issuitable in debris infested Waters and obviates the possibility of anydebris lodging in the recesses at the side portions. Actually, thislower front end may be vertical or slant toward the rear at the bottom.

The actual wall configuration of the tubular rudder includes, besidesthe aforementioned straight-sided exterior surface 22, an interiorsurface which is of a generally airfoil configuration. Thus, the forwardor leading side of the interior surface is outwardly flaring and curvedat 27, after which toward the rear the curvature straightens out into astraight side 2S, which provides a constant diameter bore to the rearend 21. The extent of the curvature of the surface 27 is fairlysubstantial along the axis of the rudder so as to provide a goodlyamount of surface more nearly perpendicular to the propeller race thanwall 2S when the rudder is turned in a hard-over position such as shownin Figure 3.

Although the propeller race has been described as being substantiallycylindrical in the description above, in actuality it may be consideredto be somewhat flattened out at the bottom. Thus, due to pressuredifferentials which increase with the distance below the surface,namely, about 0.44 p. s. i. for each foot of depth in fresh water, thereis a greater exterior pressure on the propeller race at the bottom whichcauses a partial attening out, as shown in Figure 5. The force lineswhich are greater at the bottom, as shown in Figure 5, cause thedistortion of the propeller race to be shaped as shown. ln order toenclose and mate as fully as possible with this configuration of thepropeller race, a tubular rudder having an internal cross section of thesame general configuration as that shown in Figure 5 is shown in Figures6 and 7. The modified rudder is indicated at 30 and is alike in allrespects to the generally cylindrical shaped rudder 14 except for itscross section at the front end, and like numbers have been given forlike elements.

In the modified tubular rudder 30, full acceptance and enclosure of thepropeller race is eiected with a maximum attainment of operatingefficiency. Thus, there is no obstruction and consequently nodeleterious turbulence presented in the tubular rubber to the ow of thepropeller race passing through it. Although this form of the rudder issomewhat more difficult to construct, its operating ad-y vantages areimproved over the rudder 14.

In this rudder the front end 31 is of the partially flattenedconguration shown conforming with the wheel race in Figure 5. Thisconfiguration is then changed within the rudder to the circular open end21 as this shape is most eflicient for the race exhaust in the benefitsto be derived from this invention.

The dimensioning of the rudder 14 and rudder 30 is substantially thesarne with respect to relative spacing behind the propeller blade. Thus,for rudder 14, as has been previously mentioned, the internal diameterof the circular rudder wall 28 at the rear end is approximately to 90%of the diameter of the propeller 11.` In the rudder 30, thecross-sectional area at the front end is the same as that for the rudder14. However, since the configuration is changed somewhat, the major axisat the front end is greater than the internal diameter of wall 2S andmay be increased up to approximately the diameter of the propeller whilethe minor axis is less and may be about 75 to 85% of the propellerdiameter. The most desirable length of the rudder from the front, i. e.,be-

tween top and bottom portions 24 and 213 and the end 2l, isapproximately equal to the diameter of the propeller. It will, however,beunderstood that this invention is not limited to these figures since,as has been previously mentioned, propeller design and operationalrequirements may provide differentdinien'sions, as will be understood inthe art.

With respect to the spacing between the propeller and the pivot point ofthe rudder stem l5, therev should be a distance about equal to theinternal diameter of the rudder Wall 28. However, this Yspacing iscontrolled somewhat by the length of the fairwater, and thev longer thefairwater the greater is the spacing, and vice versa for shorterfairwaters.

The recessed sides 25v and 26 of the front of the tubular rudder arecut. back from the top and bottom portions 23 and 24, respectively,about one-third of the internal diameter of theA rudder as defined bythe wall 28. This amount of recess is variable, as will be understood inthe art. However, for the instant rudder which permits of turning about35 away from the straight-forward position, either port or starboard,this has been found to present a full access of the propeller race tothe rudder so that greater maneuverability and steering control areobtained together with increased thrust in a very advantageous manner.

In Figure 8, there is shown still a further modification of thisinvention where a backing rudder 40 is supported forwardly of thevpropeller lll on a vessel 41. This backing rudder is in addition to thepreviously described stern rudder 14v (which here, is slightly modifiedby slanting lower front end 29)., or where desired, the modified rudder30, and can even be used with blade rudders. The rudder 4tlis pivotedfrom a rudderstem 42 and may be of a design like the rudder 1.4, 1,4' orthe rudder 30. The propeller shaft 12 fits entirely through the backingrudder so that the backing rudder may be turned within limits defined byits contact withy the propeller shaft 12. Where desired, stop means maybev provided with the rudder control so as to prevent actual engagementof the rudder with the propeller shaft.

It will be noted that inthe modification of Figure 8 substantially fullaccess andflow of water to the propeller is provided whether thepropeller is used in forward or reverse, since water flows througheither the rudder 40 in the forward positionor through rudder. 14 in thereverse position. The only change in this rudder. is that thecrosssectional area of its opening is slightly increased by the area ofthe propeller shaft since the wheel race of necessity flows around thisand cannot retract. to its full extent.

Operation For a full and complete understanding of this invention aconsideration should be given to the nature ofthe propeller race. It hasbeen found, that the propeller race is propelled aft of the propeller inthe general form of a cylindrical jet at a very high velocity withrespect to the surrounding water. The propulsive force of this jet onthe water from the propeller and aft of it furnishes the reactionrequired to propel the vessel forwardly. The force lines of this jetstream aft of the propeller are generally shown in Figure 2 where thenecking-downfeature to the constant diameter at point 17 has beenpreviously discussed. Actually, this is a rotating column of water in alike manner to a screw due to the rotational effect of the propeller 11.

The increase in velocity of the water propelled through this screw as itrapidly rotates causes a decrease in pressure in accordance with theBernoulli theorem. Simultaneously with this increase in velocity anddecrease in pressure, there are serious cavitation effects and internalturbulence within the propeller race. All of these factors contribute toa very turbulent wash or roll at the water surface aft of the vessel.However, with the tubular rudder 14 yor Si) of this invention asutilized, the propeller race is enclosed and the full benefit and effectof the propulsion or thrust of the race is realized without any outsideinterference or disturbance. Thus, as shown in Figure 2 where thepropeller race is enclosed, there is protection against outsideinterference from the undisturbed water medium surrounding the racewhich is at a higher pressure than the propeller race within the rudder.By enclosing thepropeller race as s hown,` a full control can be had andthe thrust is more efficiently utilized in 'a manner similar to a jetpropulsion where there is very little` inefcientdissipation of the highvelocity. race.

In Figure 3, there is shown the action of-` the propeller race within.the rudder. 1.4 when it is turned over tothe hard port position. Inthis. condition, the force lines on the starboard side impinge. againstthe open flared internal side of the airfoil section 27 of the rudderand through, a substantially normal or Vertical impingement tend tocausetherudder. topivoty in the clockwise. position about the rudder stem.Thisv action is counter-balanced by the force linesV ontheport side`which, due to the. airfoill or outwardly flaring front portion, causes aslight vacuum on the inside ofthe straight. wall 28, as is shown in thedotted lines, to create anl area of reduced pressure. This area of.lreduced pressure tends to cause a counterclockwise rotation of therudder about the rudder stem so that there are equal and opposite forceswhich tend to maintain. the rudder in the position to which itvr isturned.

The particular :nii/.antagey of this invention can be readily,understood when compared with the operation ofl astandardstraight-,bladed rudder. In such a bladed rudder, there are aA series ofirregular forces upon the rudder since it isdisposed vertically directlybehindL the propeller wheel. There. areliute cycle vibrations as thepropeller race is propelled aft of the propeller in the aforementioned.screw-like2 or spiral direction, and since the rudder is righrinthecenter there is a positive force on oneY side andi a negative forceor area 0f;.reduced;

pressure on the other sideas each flute passes the rudder. Thus, in thecase of the commonblade rudder, there are two flute cycle vibrations,one at the top of the rudder and one at.- the bottom ofthe rudder aseach flute passes the leading edge of the rudder. This not only causestorque on the rudder, but imparts a very substantial force. or vibrationv to the rudder and through it to the entire ship.

Further, since the blade rudder is placed directly. in.

the path of the wheel race, it causes a break-up or loss of the smooth,even configuration of the propeller race, and a4 great turbulence.

forward position so that this turned position is difficult.- to maintainandrequiresa substantial amount of force,

or. torque.

v In the casev of the Kort` rudder andl other propeller` shroudedrudders, therey aredisadvantages since the vfull effect of the propellerrace is lost as this race is not enclosed and controlled as has beendone in this invention. Further, in addition to the loss in thrust andgreater steering force required, relative to the present invention, thepropeller shrouded rudders are disadvantageous because of the smallclearance they have around the propeller and their increased draft.These rudders have been found to be susceptible to breakage sinceforeign objects, which inevitably are drawn into the propeller, tend tojam the clearance space on the outside of the propeller and are caughttherein which causes breakage and disrepair of the blades of thepropeller and the rudder.

Likewise, due tothe relationship of the bladed rudder directly in thepath of theV Because of the comparative considerations discussed above,it has been found that the tubular rudder of this invention has greatlyimproved maneuverability over the blade rudder, through response tocontrol and force or torque required, in the amount of 70%. Vibration inthe employment of the rudder of this invention over the blade rudder hasbeen extremely reduced and the forward thrust has been improved as muchas 10%. Also, the wheel wash leaving the tubular rudder is smoother orflatter and causes less turbulence at the surface of the water so as togreatly reduce hazards to small boats in the neighborhood.

Experiments with the tubular rudder have also been made with respect tothe Kort rudder where it has been found that steering maneuverabilityhas been increased by about 10% and the vibration has also been verysubstantially reduced. Further, the thrust from the rudder of thisinvention has been increased by approximately 10% over the Kort rudder.

The rudder 30 of Figures 6 and 7 operate in the same manner as describedabove for the rudder 14 or 14. However, in the case of the rudder 30,the operational advantages will be even greater since the capture of thepropeller race is more perfectly effected, which is the primeconsideration of this invention. As has been previously discussed, thepropeller race actually is attened out somewhat at the bottom due to anincrease in pressure which varies directly with the depth below thesurface of the water. This consideration is greater in deep draft andlarge vessels using propellers of substantial dimensions. In suchvessels, where maximum thrust steering efciency and maneuverability arevery important, the rudder 30 has its greatest application. Such demandson large vessels as large ocean-going ships or river tow-boats of greatpower which are designed to push a number of barges make practical themanufacture of this specially shaped rudder, although this rudder issomewhat more difficult to fabricate than the cylindrical shaped rudder14.

The backing rudder of Figure 8 operates in the same manner as abovedescribed for either the rudder 14 or the rudder 30 and can be made in amanner similar to either of these rudders. When a backing rudder isutilized, it surrounds the propeller shaft and, as previously mentioned,can be turned within the limits of contact with this shaft to effectsteering or maneuvering of the vessel when the propeller is reversed.Since the regular rudder 14 is tubular, it provides substantially fullaccess of llow of water to the propeller 11, which then has itspropeller race projected through the tubular rudder 40 which controls inthe manner above described.

Maintenance of the propeller and its shaft for vessels equipped with therudder invention herein disclosed is especially easy and expeditious toeffect. To remove the propeller shaft and propeller, the rudder 14 ineither Figure 1 or Figure 8 need not be removed since the propeller canbe loosened from its shaft, and the shaft, after the removal of thepropeller, can then be withdrawn 6() through the bearing 13 out throughthe rear end 21 of the rudder. The rudder need not be touched at all inthe propeller and shaft removal operation, which is of great advantageover the common blade rudder.

It is obvious that various changes and modiiications may be made in thisinvention as will be apparent to those skilled in the art. Such changesare within the scope of this invention as defined by the claims appendedhereto.

What is claimed is:

1. A rudder for marine vessels adapted to be used in spaced relationbehind a propeller on the vessel, said rudder comprising a hollow shellcompletely open and unobstructed at its front and rear ends, said shellhaving a continuous wall at its top, bottom and sides to define a hollowspace enclosed by said shell, said hollow space being slightly smallerthan the diameter of the propeller with which the rudder is adapted tobe used, said top, bottom and side walls defining a substantiallycylindrical shell, and pivot means whereby the rudder can be pivoted,said shell having its side walls at the front end recessed rearwardly ofthe front top and bottom walls.

2. A rudder for marine vessels adapted to be used in spaced relationbehind a propeller on the vessel, said rudder comprising a hollow shellcompletely open unobstructed at its front and rear ends, said shellhaving a continuous Wall at its top, bottom and sides to define a hollowspace enclosed by said shell, said howwol space being slightly smallerthan the diameter of the propeller with which the rudder is adapted tobe used, said top, bottom and side walls defined a shell having a frontopening of rounded cross section, said cross section being substantiallycircular at the top and sides and somewhat flattened at the bottom.

3. In combination with a vessel having a bladed propeller, a hollowbacking rudder for steering the vessel when the propeller is reversed,said rudder being spaced forward of the propeller and being open at itsopposed ends to receive and exhaust the propeller race when thepropeller is operated in reverse, and to pass water therethrough with aminimum of flow restriction when the propeller is operated in forward.

4. In combination with a vessel having a bladed propeller, theimprovement comprising a hollow rudder, said rudder being spaced aft ofthe propeller, said rudder having an open front end to receive saidpropeller race and an open rear end to exhaust the race, a hollowbacking rudder for steering the vessel when the propeller is reversed,said rudder being spaced forward of the propeller and being open at itsopposed ends to receive and exhaust the propeller race when thepropeller is operated in reverse, and to pass water therethrough with aminimum of flow restriction when the propeller is operated in forward.

References Cited in the le of this patent UNITED STATES PATENTS 899,359Wadagaki Sept. 22, 1908 2,139,594 Kort Dec. 6, 1938 2,601,837 Dean July1, 1952 FOREIGN PATENTS 677,849 Great Britain Aug. 20, 1952 740,224Germany Oct. 14, 1943

